Abstract:

The Hongshanzui oilfield is a typical weathering crust reservoir in the Junggar Basin, and has substantial prospect for exploration. This study uses macro-/micro-lithological and mineral analyses, geophysics, geochemistry and other experimental techniques to comprehensively study the petrological and structural features and controlling factors of igneous rocks at Hongshanzui. The results show that:(1) There are six types of igneous rocks at Hongshanzui: intrusive rocks, subvolcanic rocks, volcanic lava, pyroclastic lava, pyroclastic rock and sed-volcanic pyroclastic rock, among which andesite and tuff are the most developed; (2) Reservoir space combination of igneous reservoir includes primary pore-dissolution pore-level I, dissolution pore-level I /Ⅱ, level Ⅲ and level IV fracture types, with the physical properties deteriorate from level I to IV reservoirs; (3) The weathering crust develops a five-layer structure from top to bottom: hydrolysis zone, leached zone, break-down zone I, break-down zone Ⅱ and the underlying bedrock. The hydrolysis zone on the top is commonly decomposed into a dense soil layer, which can serve as a cap. Besides, the leached zone and the break-down zone I show better weathering and leaching transformation, hence the reservoir has the best physical properties; (4) Different oil and gas productivity wells have a good corresponding relationship with the weathering crust structure, which can guide the division of the dominant zone for the weathering crust igneous rock reservoir and the related productivity prediction.

Key words: Hongshanzui oilfield, Carboniferous, volcanic, weathering crust reservoir, productivity